1. Field of the Invention
In general, the present invention relates to a gateway. More particularly, the present invention relates to a transmission service between telephone exchanges through the Internet.
2. Description of the Related Art
In recent years, with the progress of the network technology observed mainly as the wide-band of the LAN and the progress of the PC technology evidenced mainly by the increasing versatility of personal computers (PCs) and the increasing speed of CPUs, it has become possible to put transmission of audio data between PCs of a plurality of LANs at a high speed to practical use. By virtue of these technologies, it is possible to rapidly introduce application software and systems for transmitting sounds, which used to be transmitted by the conventional phones, between PCs on the Internet comprising LANs and WANs. Such a system is referred to as an Internet telephony. In addition, there has also been developed an Internet-telephony gateway for implementing internetwork communications between a telephone network and the Internet. Such an Internet-telephony gateway has a gateway function for conversion of the protocol of the telephone network into the protocol of the Internet or vice versa. In addition, there is also a system for relaying a communication between telephone exchanges by using an Internet-telephony gateway. Such a system is known as a bypass by an Internet telephony.
In general, a telephone conversation through a bypass by an Internet telephony costs less than a telephone conversation through the telephone network. For this reason, the bypass system and its services are becoming popular very fast. So far, there has not been established a technology of a transfer service for transferring a call from a terminal accommodated in a telephone exchange of a bypass system using an Internet-telephony gateway to a terminal accommodated in another telephone exchange in a conversation. In the use of a transfer function of a telephone exchange simply for implementation of a transfer service in a bypass system using an Internet-telephony gateway, the following problems are encountered.
FIG. 32 is a diagram showing a problem encountered in the conventional system. Assume that, while a terminal 4#A accommodated in a telephone exchange 2#1 is having a conversation with a terminal 4#B of a telephone exchange 2#2, a transfer service from the terminal 4#A to a terminal 4#C of the telephone exchange 2#2 is simply executed. In this case, the transfer service is executed as follows.
At the terminal 4#A, a transfer button is pressed and the number of the terminal 4#C is dialed while the terminal 4#A is having a conversation with the terminal 4#B. The telephone exchange 2#1 transmits a call signal to the telephone exchange 2#2 by way of a gateway 6#1, the Internet 8 and a gateway 6#2, calling the terminal 4#C and establishing a connection with the terminal 4#C. As a result, 2 paths are stretched over the Internet 8 for the terminal 4#A to be used in conversations with the terminals 4#B and 4#C. When the terminal 4#A is cut off from communication (put in an on-hook state), the telephone exchange 2#1 connects the path connected to the terminal 4#B and the path connected to the terminal 4#C. In this state of connection, a transfer service is rendered between the terminals 4#B and 4#C through the telephone exchange 2#2, the gateway 6#2, the Internet 8, the gateway 6#1 and the telephone exchange 2#1. At that time, Internet lines which are not actually required are used by the telephone exchanges 2#1 and 2#2 wastefully. In addition, audio data generated by the terminals 4#B and 4#C are subjected to audio encoding and audio decoding in the gateways 6#1 and 6#2 under audio CODEC control and compressed audio data is transmitted through the Internet 8. As described above, the Internet lines are used wastefully and, in consequence, unnecessary audio CODEC control is executed on audio data exchanged by the gateways 6#1 and 6#2. As a result, there is raised a problem of a deteriorating audio quality.
It is thus an object of the present invention addressing the problems described above to provide a gateway that is capable of connecting paths effectively during a transfer through the Internet, efficiently utilizes an Internet line and does not wastefully execute audio CODEC control.
In accordance with one aspect of the present invention, there is provided a gateway connected to the Internet and a telephone exchange accommodating a plurality of terminals and carrying out routing optimization processing based on a first message used as a request for path optimization, the gateway comprising: a call setting means for: determining an IP (Internet Protocol) address of a second gateway corresponding to a calling-destination special number of a called telephone exchange used as a called communication partner and connected to the second gateway on the basis of a second message which is received from the connected telephone exchange, includes the calling-destination special number of the called telephone exchange and a telephone number of a called terminal accommodated in the called telephone exchange and serves as a request for call setting; and transmitting a third message serving as a request for the call setting to the second gateway serving as a communication partner by using the IP address by way of the Internet to open a control channel to the second gateway; a first message transmitting means for setting a fourth message received from the connected telephone exchange in a message to be transmitted by using the control channel and transmitting the message to the second gateway serving as a communication partner by way of the Internet; a second message transmitting means for extracting a fifth message and transmitting the fifth message to the connected telephone exchange when receiving a message coming from the control channel and including the fifth message set therein and transmitted by the called telephone exchange; an audio-channel opening means for opening an audio channel for a conversation between a calling terminal accommodated in the connected telephone exchange and the called terminal when receiving a message including a set sixth message issued by the called telephone exchange serving as a called communication partner through the control channel in response to the third message; and a channel releasing means for releasing the control channel and the audio channel when receiving a message including a set seventh message serving as a request for releasing of the control channel and the audio channel from the control channel.
In accordance with another aspect of the present invention, there is provided a gateway connected to the Internet and a telephone exchange accommodating a plurality of terminals and carrying out routing optimization processing based on a first message used as a request for path optimization, the gateway comprising: a call setting means for: determining an IP (Internet Protocol) address of a second gateway corresponding to a calling-destination special number of a called telephone exchange used as a called communication partner and connected to the second gateway on the basis of a second message which is received from the connected telephone exchange, includes the calling-destination special number of the called telephone exchange and a telephone number of a called terminal accommodated in the called telephone exchange and serves as a request for call setting; and transmitting a third message serving as a request for the call setting to the second gateway serving as a communication partner by using the IP address by way of the Internet to open a control channel and a first audio channel to the second gateway; a first message transmitting means for transmitting a fourth message received from the connected telephone exchange by using the first audio channel to the second gateway serving as a communication partner by way of the Internet; a second message transmitting means for extracting a fifth message and transmitting the fifth message to the connected telephone exchange when receiving the fifth message transmitted by the called telephone exchange through the first audio channel; an audio-channel opening means for opening a second audio channel for a conversation between a calling terminal accommodated in the connected telephone exchange and the called terminal when receiving a sixth message issued by the called telephone exchange serving as a called communication partner through the first audio channel in response to the third message; and a channel releasing means for releasing the control channel, the first audio channel and the second audio channel when receiving a seventh message serving as a request for releasing of the control channel, the first audio channel and the second audio channel from the first audio channel.
The above and other objects, features and advantages of the present invention as well as the manner of realizing them will become more apparent, and the invention itself will be best understood from a study of the following description and appended claims with reference to attached drawings showing some preferred embodiments of the invention.